TWIP case study
The young sushi consumer likely has anisakidosis. Caused by consuming the live herring worm. Supportive care usually is all that is needed. Most people believe themselves to have “food poisoning”, manage with self care and do quite well. No pharmaceutical prescribing required.
Nurse PractitionerAmarillo, TX
As soon as I heard sushi, I knew that was the source of the parasite, thanks to early episodes of TWiP. But I had to look up the nematode, because all I could think of was “askaris”. The answer is anasakis!
I already won a book, and thank you for that.
I am so happy Daniel and Christina joined the show; each made a great show even better.
Question for the hosts: Do you ask if sashimi has been flash frozen, or do you trust reputable establishments are doing that? Or do you avoid sashimi? Or pickled fish, or ceviche.
Thanks for an entertaining, informative, and occasionally incredibly moving show. (For all who are newish to TWiP, listen to Dickson’s story, starting at the 20:30 mark of TWiP 11: One times 3 million, to see what I mean.)
Dear Drs. Racaniello, Despommier, Griffin and Naula,
It’s currently 21 C (70 F) in the hospital call room I write from as a newly minted PGY-1! (I listened to the episode this morning before coming in).
For this young patient who vomited up a small, moving worm after eating sushi, I was ready to say, “anisakis!” but then the worm was only 5mm in length.
Four out of five of the worms my brain associates with fish are too long or wrong morphology: Diphyllobothrium latum (an enormously long, segmented, and very cool tapeworm, my favorite), clonorchis and opisthorchis (flukes), anisakis (a nematode around 2 cm in size). That leaves gnathostoma. Other non-fish associated worms that I’d think about are Ancylostoma duodenale (hookworm) and Strongyloides stercoralis (threadworm).
However, the clinical picture is most consistent with early gnathostomiasis (the phase before the worm moves out of the intestines to cause cutaneous manifestations. I think she could be treated with albendazole or ivermectin.
I rejected the Ancylostoma idea because I think Ancylostoma stay “hooked” to the intestines and if she did pass anything, I’d expect eggs in the stool rather than live worm in the vomit. Also, I think they cause a rash if I’m not mistaken.
I rejected Strongyloides stercoralis because these worms track under the skin (visibly!) and people can see them and say they itch terribly, also I think they migrate through the lungs so I would have expected her to complain of cough.
The only bad thing about seeing a new TWiP episode is that it means I have to wait an entire month for the next one. Thank you for making learning so fun!!!
This case seems like a classical case of anisakid food poisoning
treatment is albendazole 400 mg orally twice daily for one week
The Japanese government has a interesting flyer about ways to prevent getting sick off fish – I paraphrase it below:
Cooking with heat is the most effective means of prevention.
Freezing for at least 24h at -20° C (until the center of the meat is frozen) will kill Anisakis. Note however, that wasabi, soy sauce, vinegar, and other condiments will not kill Anisakis in the amounts normally used in cooking.
When making vinegared mackerel, one means of preventing Anisakis infection is to freeze the meat for at least 24 hours at -20° C (until the center of the meat is frozen) after salting and vinegaring the fish.
Do not eat fish organs raw.
When planning on eating raw fish, choose fresh products, remove internal organs as quickly as possible, and store seafood at low temperatures (4° C or less).
Hope all is going well, Anthony
Dear Drs. Naula, Racaniello, Despommier and Griffin.
I discovered This Week in Parasitism over a year ago, as a spinoff from TWIV, and now I am hooked to both programs. However, this is the first time I am writing to you, in response to the case study about a woman in her twenties who vomits a small worm after eating sushi.
I was almost led into confusion by the little tricky piece of information provided by Dr. Griffin when he added the woman traveled to Kenya six months before the worm incident.
However, when examining all the pieces of information, I believe the patient did not get infected in Kenya but the United States.
After I read the CDC website and consulted the Parasitic Diseases book in PDF which is available on the Doctors Without Borders website, my best guess is that the patient ate sushi infected with Anisakis worms. These worms are present in raw or undercooked fish or squid, and therefore, can be found in sushi.
I could not tell, or imagine, whether she ingested only one worm, and I could not find any references in the literature about how likely is it to ingest only one worm when eating raw fish infected with Anisakis worms. In any case, I hope she was lucky enough to expel all the worms she ate when she vomited. This is because, when worms are not vomited, they can invade the gastrointestinal tract, die there and produce inflammation, gastric pain, nausea, and possibly, diarrhea.
According to the Merck manual and your book, the treatment consists of the physical removal of the worms. Albendazole 400 mg administered orally twice a day for 3 to 21 days is another option.
Thank you for all you do to educate the public.
Y’all, along with the TWIV team, are my favorite YouTubers.
Fred Drach, MD
First time emailer here, and it’s a near perfect 23*C & 53% humidity day here in sunny Far North Queensland, Australia.
This young and previously well woman presents with an acute episode of (I assume) epigastric pain associated with nausea and a single vomit, the vomitus of which contains a 0.5cm mobile worm. This is linked to sushi consumption earlier in the day, but the patient has also travelled to Kenya 6 months prior.
The woman is likely suffering from Anisakiasis, caused by an anisakid parasite. There seems to be few long term sequelae from this and treatment (twice daily albendazole) is not likely necessary. Follow up in a few weeks to ensure no residual symptoms (EG; abdominal pain) would seem appropriate however. If this woman is a regular at said restaurant (or eats a lot of sushi) then maybe a hunt for ectopic infection could be worthwhile?
In terms of acquisition, the patient would have eaten the culprit undercooked or raw fish or squid within the recent hours to day. Prevention is through thorough cooking, or appropriate freezing of the food item.
I believe the travel history is a red herring*, though I am interested in hearing the approach and answers from others and the team!
*How many answers will use this phrase? I suspect them all!
Greetings from an abnormally sunny Seattle!
My guess is anisakiasis caused by the anisakid nematode. She must have ingested the larvae when she went out to eat sushi.
(P.S. I have not won a book yet)
Dear TWIP hosts,
It is a lovely 84F (29C) afternoon in Naperville Illinois. A bit too warm for my taste (I guess that is why I am living in Illinois) but I know I am a minority. Another month and another case… TWIP is the gift that keeps on giving! Still hoping for a book at some point. Wish me luck! It is a relatively short case, a woman in 20s vomited up a worm after eating sushi in a mama papa restaurant. Still moving I might add, and with horrible abdominal pain. My guess in this case is Anisakiasis caused by Anisakis. Often found in raw fish and sea mammals. According to PD 7, symptoms could include abdominal pain, nausea, vomiting, abdominal distension, mild fever and diarrhea with blood and mucus in the stool. Sometimes the worms are expelled through coughing or vomiting. It is interesting that flash freezing or cooking can prevent such infections. Did that restaurant mention “extra fresh” sushi on the menu? I recall eating sushi directly carved from a tuna while visiting Palau, it was a lovely place by the ocean and the fish it sure tasted fantastic, luckily I was fine afterwards or maybe the extra alcohol helped as well… again thank you for the show and proving such great education to the public, especially for the people who are interested but did not pursue this as a profession. (A bit of regret, have to say..)
Hope all of you have a great rest of the day and be safe!
Hello, Twip Team,
Today it is 24 degrees C and there is not a cloud in the sky. This is pretty uncommon when you live close to the mountains. To take advantage of such an event I went to the beach to watch the sunset. With the image of a glowing orb vanishing behind the horizon still on my mind, I can now think about the next case. The fact that the woman ate sushi and then developed acute abdominal pain I immediately think of Anisakis. These parasitic nematodes have a life cycle involving fish and marine mammals. We, humans, have a similar digestive system to marine mammals, but it is not similar enough for the worm to carry out its normal lifecycle. A few hours after ingesting fish containing the larval stage, it tries to burrow through the intestinal wall but cannot penetrate it. This angers the innate immune cells such as mast cells, basophils and eosinophils which release a pharmacopeia of cytokines. Inflammation and severe pain soon follow. I shake my head every time I hear about this happening, it is easily preventable. When will people learn to freeze their raw fish first or fully cook unfrozen fish? Surely this sushi joint knows better… There are other nematodes that follow the Ascaris life cycle (Hookworms, Strongyloides stercoralis, Ascaris lumbricoides) which travel up over the epiglottis. It may be possible to cough or vomit these up as well, but they are not associated with sudden abdominal pain. And I think they would be much smaller than 0.5 cm at this point in their lifecycle because they needed to travel through a hair follicle first. Except for Ascaris which is ingested and then feeds on the liver before travelling to the lungs. My notes are really lacking information on the specific sizes of these nematodes, so hopefully, someone can correct me.
Daniel from BC Canada
10 Michelle and Alexander from the First Vienna Parasitology Passion Club write:
The patient is a young woman who spent time in Kenya 6 months prior and complains of abdominal pain with vomiting after eating sushi earlier the same day. A 5mm worm was found in the vomit. While it is often useful to look for a unifying diagnosis, it is also possible that there is a distinct reason for her symptoms and that the worm was found coincidentally. Based on this information, we attempted to construct a complete differential.
Infection with Ascaris lumbricoides is the most widespread intestinal helminthosis globally and should be mentioned as a differential. Ingested eggs hatch in the duodenum, larvae then migrate through the liver into the heart and lungs via the portal vein. After attaching to the alveolar capillaries and penetrating the alveolar walls, larvae ascend the bronchial tree to the oropharynx, where they are swallowed and return to the small intestine. It is possible that Ascaris could have been coughed or vomited up coincidentally at this particular point of their life cycle. The size of Ascaris does not fit the worm described in the case and neither do the acute symptoms shortly after ingestion. Geohelminths like Strongyloides and Nercator also follow a similar path in their life cycle, but the larvae are much smaller than the worm described.
The fish tapeworm Diphyllobothrium may be mentioned as a differential, due to the fact that the transmission of this tapeworm is also owed to the consumption of undercooked and raw fish. Diphyllobothrium species do not cause the described symptoms within a few hours of ingestion. Also the size of the fish tapeworm does not fit the mentioned size of the worm the patient vomited up.
Several species of trematodes can infect the bile ducts of humans and could therefore theoretically be ejected with vomiting and could theoretically also be responsible for pain and nausea via obstruction of the bile ducts or pancreatic ducts. Opisthorchis viverrini and Clonorchis sinensis are neither found in the US nor in Kenya and should therefore be excluded. While Fasciola hepatica and Fasciola gigantica can be found in Kenya, the adults are usually quite a bit larger than 5mm and are morphologically very distinct. All of these worms are transmitted via uncooked freshwater fish in endemic regions, so this could hopefully be ruled out by taking a thorough history.
Furthermore, the possibility of an artefact should also be considered. Non-parasitic worms can be ingested by accident and can vaguely resemble a parasitic helminth. Some food items can also be mistaken for a worm. Careful macroscopic and possibly histological examination should be able to quickly rule out this possibility.
We believe that the most likely diagnosis in this case is Anisakiasis. Anisakis spp. can be found in the Pacific, Atlantic, Arctic ocean and other cold marine waters. Infectious L3 larvae measure about 2cm, which fits the size description of the worm mentioned in the case.
The life cycle of Anisakis involves crustaceans and often several fish as intermediate hosts and larger sea mammals, who ingest those fish, as definitive hosts. The L3 larvae from the fish tissue penetrate the gastric mucosa where they reside and reproduce, shedding eggs in the stool. Humans are aberrant hosts for these nematodes and the attempt of the larvae to penetrate the human gastrointestinal tract and the resulting inflammation are largely responsible for the clinical presentation.
Symptoms range from abdominalgia, nausea, vomiting, fever or diarrhoea within hours of ingesting the larvae – these symptoms are often confused with the symptoms of an acute gastric ulcer. Anasakis is usually diagnosed through endoscopy or when patients cough up or vomit up the larvae. Stool examination is not useful for diagnosis. Infections with Anisakis are often self-limiting – all anisakid worms die within a few days in humans. Larvae can be removed via endoscopy or treated orally with Albendazole 400mg once a day over a duration of 21 days. The disease can be prevented by adequately cooking or freezing seafood and abstaining from raw or marinated fish. Sushi grade fish should be flash frozen to increase safety and preserve taste and texture.
Thank you for this great case. All the best,
Michelle and Alexander from the First Vienna Parasitology Passion Club
Kia ora from Pongaroa
The young lady who ate sushi in Kenya is most likely infested with Anisakis simplex. PD7 tells me that these nematodes can infect sea mammals, crustaceans and fish. depending on the species. Symptom onset is usually quick, from minutes to hours after the ingestion of uncooked or unfrozen fish and can be so severe that it can be confused with a gastric ulcer. Nausea and vomiting, as in this case, or endoscopic removal can present evidence of the worm. It is self-limiting as they die within a few days in humans.
I note, with pleasure, that Dickson is now not the only TwiX TikTok star and now Daniel and Vincent also have videos up. So I encourage everyone who is on TikTok to follow @#microbe.tv and get science education out there on that platform.
Dear TWiP hosts, the air in DC is 545 on the Rankine scale. The barometric pressure is 1,012,000 Barye.
My guess is that the patient experienced Anisakiasis. While plenty of other parasitic worms present in the developing world could cause vomiting, they did not seem to fit the size description. The short duration from ingesting sushi to vomiting also suggests Anisakis worms (Shrestha et al. 2014).
Shrestha S, Kisino A, Watanabe M, Itsukaichi H, Hamasuna K, Ohno G, Tsugu A. Intestinal anisakiasis treated successfully with conservative therapy: Importance of clinical diagnosis. World J Gastroenterol 2014; 20(2): 598-602 Available from:
Dear TWiP Collective,
Greetings from Lower Manhattan where it is remarkably muggy, overcast and 83 degrees F (28 degrees C).
I do have a diagnostic guess for TWiP 207. I believe the patient is suffering from a parasite she encountered here at home, not in Kenya (mention of her African sojourn being something of a red herring in this mystery — pun intended, I guess).
I suspect that her locally contracted parasite came from the sushi she ate at the questionable restaurant, and that the parasite in question is Anisakis. The patient’s symptoms: sudden extreme abdominal pain experienced shortly after eating, vomiting, expelling a worm are the exact symptoms described in Parasitic Diseases. This parasite is a nematode that is found in a range of fish, many of which are typically served raw as sushi. New York City requires restaurants to follow FDA guidelines to freeze fish that is going to be served raw for 15 hours at -21 degrees F or for 7 days at -4 degrees F, but it is possible that the restaurant she went to didn’t follow the guidelines.
One thing that surprises me is how quickly the body reacts to the parasite. Unlike so many infections, the infection becomes obvious within hours. Why does this reaction happen so quickly? Is it because of the life stage of the nematode at the time it is ingested?
Treatment usually comprises removing the worm, which the patient did on her own, but which can also be done by upper endoscopy. In some case, albendazole is also prescribed. (Is this to prevent additional complications by the possibility that the initial worm was able to leave larvae behind or is there a possibility of a second infection that the albendazole is warding off?)
As always, thank you so much for your podcast and for your wonderful cases. Thank you especially recently for your interview with Claire Panosian. She was terrific and super informative, especially because I am also going to visit Hawaii and would love to avoid Rat lungworm if at all possible. (I will take her advice and avoid green juice beverages even more than I do in my regular New York City life.)
Best wishes again and many thanks
Elise (Mac Adam – in Lower Manhattan)
For this case, my guess is that Kenya is a red herring (fish pun intended) – I’d say she got anisakiasis from the sushi!
Loved this case!
All the best,
Greetings TWiP team. As always I enjoy watching TWiP even if it is monthly and not weekly. I hope I am replying in time.
The patient in case 207 is a woman who ate at a mom & pop sushi restaurant. She subsequently became ill and vomited. In the vomitus was a small worm. It is reported that a few months ago she was in Kenya. I believe the Kenya trip is a red herring. More likely the problem is a herring worm or more formally one of the members of the genus Anisakis. I think this is more likely than the fish tapeworm, Diphyllobothrium latum, which is larger.
Anisakis are yet another parasite with a life cycle involving multiple animals. The definitive hosts are cetaceans. Humans are a dead end for the worm if that’s any consolation to the patient. The worms do not live long in humans, but they may embed in gastric mucosa and require endoscopic removal. Persons may also become sensitized to worms with a resulting anaphylactic reaction.
This can be prevented by cooking, a technique developed by Homo erectus about a million years ago. Of course H. erectus is extinct, so one may choose to not follow their technique. Freezing the fish can kill the parasite. Perhaps the restaurant owners were unaware of this recommendation and took care to only serve fresh, never frozen seafood.
Best wishes to you all from a hot 102F (39C) and dry Massachusetts
The Parasitology club of the University of Central Lancashire writes:
Dear TWIP professors:
Greetings from the University of Central Lancashire situated in the beautiful northwest of England.
We would like to add our considered opinion on the case of a young woman in her 20s, recently from Kenya and who developed severe abdominal pain and vomited up a live worm of approximately 0.5cm after a sushi meal earlier that day.
The most probable cause of her condition is the nematode Anisakis, which may be ingested in raw or undercooked seafood.
Infected marine mammals release eggs into the sea in faeces. The eggs rupture to produce larvae which are ingested by crustaceans (definitive hosts). Fish are intermediate hosts which acquire them from feeding on crustaceans. Consumption of undercooked fish in foods like sushi and sashimi leads to ingestion of the larvae, which invade the gastrointestinal wall by attaching to the intestinal mucosa (Kabun, 2021). Eventually, the larvae die, causing inflammation in the stomach, oesophagus, and intestine.
Anisakiasis is majorly found in areas where there is higher consumption of raw fish such as Japan. Since consumption of undercooked fish is highly popular, anisakiasis is also common in the United States, Europe, South America, and other areas of the world. Anisakiasis can be prevented by adequately cooking the seafood to the temperature of approximately 145°F. However, for raw consumption the fish should be frozen to -35°C for 15 hrs or -20°C for 7 days. (Centre of diseases and Prevention, 2019).
The most common symptoms include abdominal pain, diarrhoea, nausea, vomiting and mild fever. These are experienced up to 48 hrs after consumption. The disease may be diagnosed by endoscopy, radiography, or surgery in the case of anisakids that have embedded in gastrointestinal tissues. Positive serological reactions aids in diagnosis. Diagnosis is carried out histologically by eosinophilic granuloma and presence of larvae with Y-shaped lateral cords (Bouree at al., 1995).
Thank you for another challenging case.
On behalf of the Parasitology club of the University of Central Lancashire
Bouree, P., Paugam, A., & Petithory, J. C. 1995. Anisakidosis: report of 25 cases and review of the literature. Comparative immunology, microbiology and infectious diseases, 18(2), 75–84.
Centre of Diseases and Prevention. 2019. Parasites-Anisakiasis [online]. Available from https://www.cdc.gov/parasites/anisakiasis/index.html. [Accessed 08th March 2022].
Kabun, R. 2021. Extraction and analytical methods for the identification of parasites in food. 2nd ed. Academic Press. Philadelphia.
I am writing in response to your Case study in TWIP 207. When I heard Mom and Pop sushi restaurant, I was immediately apprehensive. I fear that my apprehension was warranted. When you mentioned the abdominal discomfort and sushi, my mind went immediately to Anisakis spp. This was partially confirmed by the sudden onset of the distress (the sushi was ingested on the same day as symptom onset); according to my sources, gastric symptoms can develop, as soon as, a few hours post ingestion. The size of the parasite is a little low for Anisakis, but I’ll maintain my guess.
All the best,
Hello TWiP Team,
Hoping this entry makes it in on time…..As for the 20 year old female vomiting up a little wiggly-worm, I vote for Anisakiasis caused by the anisakid nematode. She likely ingested a piece of raw sushi-fish harbouring the parasite within its muscle tissue. When released into her stomach, the nematode larvae can invade the GI tract tissues, facilitated by release of parasite hydrolytic enzymes. The onset of symptoms such as abdominal pain can occur within minutes to hours of ingestion, which fits her story, and may be accompanied by nausea, vomiting, and even bloody diarrhea. In this case, the vomiting likely expelled the parasite rather quickly after ingestion and thus prevented further sequela. If the worm remains, it can invade the gastrointestinal tract. It eventually dies and then may provoke an eosinophilic granulomatous infiltration, producing an inflamed mass in the esophagus, stomach or intestine, which may lead to obstruction or peritonitis.
Diagnosis and treatment are made through removal of the parasite by endoscopy or surgery – or as in this case – the auto-ejection of a worm through vomitus. I concur with Dr. Daniel…..that my main goal would have been to reach the porcelain throne in a timely manner and it bewilders me that she somehow managed to plan and coordinate the collection of her vomitus. Kudos to her! I am not sure whether one can presume that this was the only worm that she acquired and is thus cured, or if she still requires endoscopy to be sure.
On the CDC website, they mention reports of using Albendazole 400 mg orally twice daily for 6 to 21 days in presumed diagnoses, with the caveat that this is not an FDA approved therapy.
Prevention of Anisakiases would be best achieved by the thorough cooking of fish and/or avoiding fresh sushi (which I personally love!). But freezing fish prior to serving it raw can also eliminate risk of this parasitic acquisition.
Thoroughly enjoying a breezy 74’ F (23’ C) with 55% humidity, after a few weeks of stagnant 85’ F with 100% humidity in NW Panama.
As always – so grateful for all these podcasts! Kimona
Good morning TWIP team!
My name is Chris and I am a first-year medical student at the University of California, Los Angeles. I am a long-time listener of TWIV, Immune, and now TWIP. This is mostly a thank you email because when times get tough and I lose sight of my path, I can reliably depend on the podcast to refuel my motivation to become an infectious disease doctor. You all are amazing!
I am cramming for a neurology test that is coming up so I couldn’t spend too much time thinking about the case of the woman in her 20s, who vomited up a worm. 0.5 cm in length, but my immediate guess was a nematode worm of some sort, like anisakis species or pseudoterranova spp., but mostly because I think that name is really cool.
Infectious Diseases and Vaccinology
University of California, Berkeley